Presentation on theme: "Weathering, Soils and Mass Movement BFRB Pages"— Presentation transcript:
1 Weathering, Soils and Mass Movement BFRB Pages 157 - 161 Chapter 8Weathering, Soils andMass MovementBFRB Pages
2 Weathering and Erosion Weathering - Def. - the break down of rocks that have been exposed to the atmosphere.Once the rocks are broken down, the pieces are transported from one place to another. This process is called erosion.Erosion is caused by wind, moving water (streams, waves, ocean currents), ice (glaciers), and by gravity.VIF - Most erosion that takes place on Earth is caused by moving water
3 What is W.E.D.?Weathering - the breakdown of rock into smaller pieces due to physical or chemical changes.Once the rocks are broken down, the pieces are small enough to be transported from one place to another. This process is called Erosion.Since the weathered rocks have been moved, eventually they are going to have to be dropped. This process is called Deposition.
4 Remember the Rock Cycle Diagram? Page 6 of the “Handy Dandy” ESRT’s…
5 2 Types of Weathering Physical weathering – rocks are broken down into smaller pieces without changing their chemical composition (what they’re made of).AKA - mechanical weatheringChemical weathering – rocks break down as their minerals change in chemical composition (they become different substances).
7 Types of Physical Weathering #1 - Frost action (aka Ice Wedging)water enters small cracks in the rock.when water freezes, it expands and forces the crack to open more.the ice melts back into liquid water and fills the crack again.the process repeats over and over again until the rock breaks apart.
10 Close up shows jagged rocks from FROST wedging!
11 This boulder has been split apart by frost action!!!
12 Types of Physical Weathering #2 - AbrasionIt is the physical wearing down of rocks as they rub or bounce against each other. This process is most common in windy areas, under glaciers, or in stream channels.It can also happen during rock slides (gravity)
13 Rocks that have undergone different kinds of abrasion look very differently! Rock weathered by a rockfallRock weathered by a stream
14 Types of Physical Weathering #3 Plant Roots The roots of trees often wedge in between cracks in rocks and force apart rocks even further as they grow!
17 Types of Physical Weathering #4 Animals Animals (worms, groundhogs, rabbits, etc.) burrow into the ground exposing more rock surfaces to the agents of weathering.
18 Types of Physical Weathering #5 Wetting and dryingBreaks up rocks that are made from clay.When they are wet they expand, and they shrink as they dry.As this repeats over and over, the clay becomes weak and cracks (think of all the projects you have made out of clay…they all crack and fall apart)!
24 Types of Physical Weathering # 6 - Exfoliationsoil and rock is removed (glaciers or uplifting), exposing rock found deep underground.This releases the pressure causing the surface of the rock to expand and eventually crack and flake off.
31 Agents of Chemical Weathering #2 - Plant Acids - Lichen & MossThese plants live and grow on rocks and eventually break them apart by the weak acids that they secrete!Lichen – light green/looks like bread moldMoss – dark green
33 Agents of Chemical Weathering #3 - Oxidationoxygen reacts with some minerals, especially those containing iron to form rust (called iron oxide).The rusty spots weaken the rock and it breaks apart.Water is not needed for oxidation to occur, but it does speed up the process!
37 Oxidative weathering of mineral deposits (new deposits are white/yellow, weathered deposits are reddish-brown)
38 Agents of Chemical Weathering #4 - Acids in waterCarbon dioxide, nitrogen dioxide, and sulfur dioxide dissolve in water and create carbonic acid, nitric acid, and sulfuric acid.This acidic water can cause rocks to dissolve, especially those containing calcite like limestone and marble!Acids may be found in ground water (forms caves) or in rain water (acid rain).
39 “Gnarled Rock” – a formation of limestone chemically weathered by acid rain
42 Carbonic acid in groundwater causes caves to form. When the acidic groundwater comes in contact with limestone, the limestone dissolves and caves and caverns are formed.Howe Caverns in NY and Carlsbad Caverns in NM are examples of these beautiful geologic formations
43 Carlsbad Caverns – New Mexico StalactitesStalagmitesCarlsbad Caverns – New Mexico
47 Factors that affect rates of weathering: Rock’s resistance to weathering (HARDNESS)Amount of surface areaClimate:Chemical weathering occurs faster in warm, wet climatesMechanical weathering occurs faster in cold or dry climates
48 The central area of rock was less resistant to weathering…thus the “arch” was formed! This is differential weathering.
50 Devil’s Tower, Wyoming - An igneous intrusion (volcanic neck – the underneath of the volcano) surrounded by less resistant sedimentary rock layers. Erosion has exposed this monolith! This is an example of differential weathering!!!You may recognize it if you’ve ever seen “Close Encounters of the Third Kind”
51 Surface Area Greater surface area increases the rate of weathering Surface area is the amount of rock surfaces exposed to the atmosphereWeathering creates more surface area
53 Dry Climate = Mechanical Weathering! Devil’s Marbles, Australia – Mechanical weathering from wind and sand!
54 Wet Climate = Chemical Weathering! (water speeds up chemical reactions) Water runoff seeps into the soil at the base of granite rock faces. Over time, water and permanently moist soil conditions act together to chemically weather away granite minerals such as feldspar and mica!
60 What is soil made of? Weathered rock Organic material (humus) Air Soil has 4 components:Weathered rockOrganic material (humus)AirWater
61 There are 2 types of soil…. PARENT MATERIAL is the rock that the soil forms fromWhen the parent material is the underlying bedrock of the area, the soil is called RESIDUAL SOIL (residual = what is left behind when the bedrock weathers – it still “resides” or lives with the parent material)If the soil was formed in one place and carried (transported) elsewhere (by wind, water, glaciers, etc…) then the soil is called TRANSPORTED SOILVIF - MUCH OF THE SOIL IN NYS IS TRANSPORTED SOIL LEFT BEHIND BY GLACIERS!
62 Cross section of soil layers Each layer is called a HORIZONHorizon O/A = Topsoil (mostly humus, some weathered rock)Horizon B = Mostly weathered rock, some organic material (mineral rich zone)Horizon C = Broken BedrockBEDROCK
67 LANDSLIDE (Rapid Mass Movement) Sudden movement of soil downhill (usually a very steep slope)AVALANCHE – landslide made of Ice & Snow as well as SoilSLUMP – small areas of land moving downhill - especially along roadways that cut into the side of hills
74 Even though rapid mass movement is more noticeable than slow mass movement, overall, more material is transported via creep than all others combined – because it is occurring in many more places and all the time!!!!